Which if the following most logically completes the argument?

United states manufacturers currently produce most of the world's solar-power generators-most of which are exported to Europe. However, European manufacturers are emerging and probably will ultimately capture much of the European market. The United States government is funding initiatives intended to encourage use of solar power within the United States. If these initiatives succeed in increasing the demand for solar-power generators in the United States,United States manufacturers will probably maintain significant production levels, since---------------

A) some United States manufacturers have been substantially increasing their output over the last several years.
B) the efficiency of solar-power generators in converting energy from the Sun into electric power is not improving as fast as it once did
c) Just sa European manufacturerenjoy certain advantages in Europe, so do united States manufacturers in the United States.
d) European government are currently undertaking initiatives to stimulate the use of solar power within Europe
e) the current market for solar-power generators in the United States is very limited.

Pls explain what is the correct answer and why other choices are wrong? What is the best way to arrive at the correct answer in these types of question?

ok, one thing should be clear at the outset: you're trying to fill in a gap in the logic. (in fact, there's a literal gap to fill in!)

here's a diagram type thingy:
euro companies emerge
AND
euro companies take over euro market
AND
u.s. market emerges
AND
----
THEREFORE
u.s. companies will replace euro market sales with u.s. market sales

we currently have facts asserting that the u.s. firms will lose their hold on the euro market. however, we have nothing asserting that the u.s. firms will gain a hold on the u.s. market, the second half of the conclusion.

therefore, we need an assertion that says, or implies, that the u.s. firms will gain a hold in the u.s. market (i.e., the euro firms won't take over the u.s. market as well).

(a) irrelevant:
- recent increases are unrelated to maintaining production in the future
- recent increases in production have nothing to do with the main logic gap (ensuring that u.s. firms will have a hold on the u.s. market)

(b) irrelevant:
- this has nothing to do with anything related to the argument

(c) correct
this statement strongly suggests that the u.s. firms will dominate the u.s. market for the same reasons that the euro firms will dominate the euro market.

(d) doesn't help
- we know that the u.s. firms will lose the euro market anyway, so it doesn't matter whether that market grows or not

(e) WEAKENS the argument
- if the u.s. market is very small, then it's likely that the production/revenue/etc of u.s. firms will decline rather than stay constant.

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as far as you query 'what is the best way to arrive at the correct answer': there's clearly not an extremely simple way, since gmac would not bother writing these questions if there were. the best way to figure out the underlying logic is to make a diagram (like the one i made above, with the ands and therefores), which will force you to map out the logic.